The invention relates generally to the art of thermochemical hydrogen production.
Hydrogen is considered to be an attractive energy source for development to replace fossil fuels, which are being consumed rapidly and becoming increasingly expensive. The combustion of hydrogen produces no obnoxious products and therefore causes no insult to the environment.
Technology is presently available for adapting existing energy transport means and consuming equipment for hydrogen utilization. Natural gas pipelines, for example, can be converted to hydrogen-carrying pipelines with minor modifications. Experimental automobiles, with modified conventional internal combustion engines, can use hydrogen for fuel.
As the prospect of hydrogen utilization becomes increasingly likely, methods for producing hydrogen need to be upgraded and increased. The conventional source of hydrogen has been electrolysis of water. Electrolysis, however, is highly inefficient owing to inefficiencies of electricity production and a maximum efficiency of about 80 percent for electrolysis. Electrolytic production of hydrogen is limited by the overall futility of using one energy source, typically fossil fuels, at the point of electricity production to produce hydrogen at the point of electrolysis. The disadvantages of using irreplaceable fossil fuels are obviously not overcome by such a process.
Chemically feasible processes for the direct conversion of fossil fuels and water to hydrogen are available and overcome many of the inefficiencies and disadvantages of electrolysis. However, prudence dictates that fossil fuel consumption should be minimized and the fuels conserved for use as chemical intermediates.
Thermochemical processing is therefore a most attractive method for producing hydrogen. By this technique, water is broken down to hydrogen and oxygen in a series of chemical reactions not involving the use of fossil fuels. This series of reactions is preferably carried out in a closed cyclic manner in which all products except hydrogen and oxygen are recycled as reactants. One such process, disclosed in U.S. Pat. No. 3,490,871, utilizes the reaction of cesium with water to release hydrogen.
Another such process, disclosed by Grimes et al in U.S. Pat. No. 3,919,406, involves the reaction of copper and magnesium chlorides with water to produce hydrogen in a cyclic manner.
Another such process is disclosed by Bamberger et al in U.S. Pat. No. 3,927,192. The process therein disclosed comprises reacting chromium oxide with an alkali metal hydroxide to produce hydrogen, water and alkali metal chromate as reaction products.
Bamberger et al (U.S. Pat. No. 3,929,979) also disclose a cyclic process for splitting water, wherein magnetite is reacted with an alkali metal hydroxide to give hydrogen, alkali metal ferrate and water as products.
Bamberger et al, in U.S. Pat. No. 3,996,343, disclose the production of hydrogen in a closed chemical cycle for the thermal decomposition of water by reaction of water with chromium sesquioxide and strontium oxide.
Bamberger et al (U.S. Pat. No. 4,005,184) employ chromium and barium compounds in a thermochemical process for producing hydrogen using barium and chromium compounds.
Ishii et al (U.S. Pat. No. 4,098,875) produce hydrogen thermochemically from water using tri-iron tetraoxide and hydrogen bromide as the main cyclic reaction media. The use of barium iodide, carbon dioxide and ammonia as cyclic reaction media is disclosed in U.S. Pat. No. 3,996,342.
The reaction of cerium compounds with sodium phosphate and sodium carbonate in a thermochemical cycle for producing hydrogen from water or carbon monoxide from carbon dioxide is set forth in commonly assigned application Ser. No. 50,379 filed June 20, 1979.
It has also been proposed in commonly assigned application Ser. No. 47,447, filed June 11, 1979, to produce hydrogen thermochemically in a cyclical process using cerium-oxygen-titanium compounds.